Using the same figures as in my above post for pistons, gaskets, etc., but with 76 cc heads, the static compression ratio would be 8.74:1. With that cr, I'd run a cam something like this:
It's doubtful you're gonna make 300 horsepower with this combination though. It would just be a real nice daily driver type motor. Using 1.6 rockers on both intake and exhaust would yield a theoretical valve lift of 0.469". This cam is ground on a lobe separation angle of 110*. If you wanted a little more rump at idle, you could have it ground on 106* angle. It's a single pattern cam. You may want to look around for a dual pattern cam if you think it would help the exhaust side of the motor with stock heads. I'd be just as happy with a single pattern with this particular combination. Here's a dual pattern cam that is ground on 112* angle just so you can compare cams.
Do not cut a check for a cam based on the information I've provided here. ALWAYS CALL YOUR FAVORITE CAM GRINDER FOR A DEFINITE RECOMMENDATION. I'm just trying to give you an idea of cams that would work with the info you've provided. A narrower angle such as 106* will give you a rump-rump idle and build good bottom end, but will peak quicker and lay down on the top end. A narrow angle may not provide enough manifold vacuum to operate power brakes properly. A wider angle such as 112* will give a smooth idle and excellent manifold vacuum for power brakes and such and will be stronger on the top end without giving up much on the bottom.